Interannual and interdecadal variability of the number of cold days in Hong Kong and their relationship with large-scale circulation

During the past decade (2004/05-2013/14), the number of cold days in Hong Kong (N_CD), as a proxy of the temperature of southern China, appeared to have increased from the historical minimum, in contrast to a remarkable decline in the entire postwar period. This is related to the recent apparent changes in the largescale circulation upstream and downstream of the East Asian winter monsoon (EAWM) region: the increase in Ural blocking (UB) that enhances cold advection from the polar region and reinforces the Siberian high and the decrease in a western Pacific (WP)-like index that corresponds to increasing meridional gradient of geopotential height over the EAWM region. Overall, UB and WP account for 26.4% of the interannual (≤8 yr) variance and 83.7% of the decadal (>8 yr) variance of N_CD for the period 1948/49-2013/14, indicating that further study could lead to improvement in the prediction of N_CD.